Field of the Invention
The present invention relates primarily to a process for preparing certain phosphorus-containing cyanohydrins of the formula (I) defined below, and also to certain phosphorus-containing cyanohydrins per se and to their use for the preparation of glufosinate and/or glufosinate salts. The present invention further relates to certain mixtures particularly suitable for preparing the phosphorus-containing cyanohydrins of the formula (I) defined below.
Description of Related Art
Phosphorus-containing cyanohydrins are useful intermediates in a variety of subject fields, more particularly for the production of biologically active substances which can be used in the pharmaceutical and/or agrochemical sector.
U.S. Pat. No. 4,168,963 describes diverse phosphorus-containing compounds with herbicidal activity, of which, in particular, phosphinothricin (2-amino-4-[hydroxy(methyl)phosphinoyl]butanoic acid; common name: glufosinate) and its salts have acquired commercial importance in the agrochemistry (agricultural chemistry) sector.

Methods for producing intermediates for the synthesis of phosphorus-containing compounds of this kind with herbicidal activity, more particularly glufosinate, are described in U.S. Pat. No. 4,521,348, DE 3047024, U.S. Pat. No. 4,599,207 and U.S. Pat. No. 6,359,162B1, for example.
CN 102372739A describes a process for preparing glufosinate by reacting (3-cyano-3-hydroxypropyl)-methylphosphinic acid with carbon dioxide, ammonia and water.
CN 102399240A discloses processes for preparing glufosinate and glufosinate analogs, the starting materials therein including PCl3, CH3MgCl and certain trialkyl esters of phosphorous acid. The dialkyl methylphosphonates and alkyl methylphosphinates prepared therefrom are subsequently reacted therein by Michael addition and further reaction steps to form glufosinate and glufosinate analogs.
CN 101830926A relates to the preparation of dialkylmetal phosphinates and to the use thereof as flame retardants. In the process described, alkyl phosphinates are reacted with terminal olefins, the reactions including that of monobutyl methanephosphinate with cyclohexene.
The processes from the prior art for preparing phosphorus-containing cyanohydrins have disadvantages: for example, an inadequate yield of phosphorus-containing cyanohydrins, an excessive fraction of co-products or secondary products, an excessive cost and complexity in purifying and/or isolating the phosphorus-containing cyanohydrins, and/or reaction conditions which are too harsh or too difficult in terms of process and/or equipment.